Fix and simplify some usages of TimestampDifference().

Introduce TimestampDifferenceMilliseconds() to simplify callers
that would rather have the difference in milliseconds, instead of
the select()-oriented seconds-and-microseconds format.  This gets
rid of at least one integer division per call, and it eliminates
some apparently-easy-to-mess-up arithmetic.

Two of these call sites were in fact wrong:

* pg_prewarm's autoprewarm_main() forgot to multiply the seconds
by 1000, thus ending up with a delay 1000X shorter than intended.
That doesn't quite make it a busy-wait, but close.

* postgres_fdw's pgfdw_get_cleanup_result() thought it needed to compute
microseconds not milliseconds, thus ending up with a delay 1000X longer
than intended.  Somebody along the way had noticed this problem but
misdiagnosed the cause, and imposed an ad-hoc 60-second limit rather
than fixing the units.  This was relatively harmless in context, because
we don't care that much about exactly how long this delay is; still,
it's wrong.

There are a few more callers of TimestampDifference() that don't
have a direct need for seconds-and-microseconds, but can't use
TimestampDifferenceMilliseconds() either because they do need
microsecond precision or because they might possibly deal with
intervals long enough to overflow 32-bit milliseconds.  It might be
worth inventing another API to improve that, but that seems outside
the scope of this patch; so those callers are untouched here.

Given the fact that we are fixing some bugs, and the likelihood
that future patches might want to back-patch code that uses this
new API, back-patch to all supported branches.

Alexey Kondratov and Tom Lane

Discussion: https://postgr.es/m/3b1c053a21c07c1ed5e00be3b2b855ef@postgrespro.ru

2 files changed, 5 insertions, 28 deletions

diff --git a/src/backend/replication/walreceiverfuncs.c b/src/backend/replication/walreceiverfuncs.c
index 67b1a074cce..da07088b425 100644
--- a/src/backend/replication/walreceiverfuncs.c
+++ b/src/backend/replication/walreceiverfuncs.c
@@ -320,10 +320,6 @@ GetReplicationApplyDelay(void)
 	WalRcvData *walrcv = WalRcv;
 	XLogRecPtr	receivePtr;
 	XLogRecPtr	replayPtr;
-
-	long		secs;
-	int			usecs;
-
 	TimestampTz chunkReplayStartTime;
 
 	SpinLockAcquire(&walrcv->mutex);
@@ -340,11 +336,8 @@ GetReplicationApplyDelay(void)
 	if (chunkReplayStartTime == 0)
 		return -1;
 
-	TimestampDifference(chunkReplayStartTime,
-						GetCurrentTimestamp(),
-						&secs, &usecs);
-
-	return (((int) secs * 1000) + (usecs / 1000));
+	return TimestampDifferenceMilliseconds(chunkReplayStartTime,
+										   GetCurrentTimestamp());
 }
 
 /*
@@ -355,24 +348,14 @@ int
 GetReplicationTransferLatency(void)
 {
 	WalRcvData *walrcv = WalRcv;
-
 	TimestampTz lastMsgSendTime;
 	TimestampTz lastMsgReceiptTime;
 
-	long		secs = 0;
-	int			usecs = 0;
-	int			ms;
-
 	SpinLockAcquire(&walrcv->mutex);
 	lastMsgSendTime = walrcv->lastMsgSendTime;
 	lastMsgReceiptTime = walrcv->lastMsgReceiptTime;
 	SpinLockRelease(&walrcv->mutex);
 
-	TimestampDifference(lastMsgSendTime,
-						lastMsgReceiptTime,
-						&secs, &usecs);
-
-	ms = ((int) secs * 1000) + (usecs / 1000);
-
-	return ms;
+	return TimestampDifferenceMilliseconds(lastMsgSendTime,
+										   lastMsgReceiptTime);
 }
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 92bc6577848..b6c456f0c5a 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -2033,8 +2033,6 @@ WalSndComputeSleeptime(TimestampTz now)
 	if (wal_sender_timeout > 0 && last_reply_timestamp > 0)
 	{
 		TimestampTz wakeup_time;
-		long		sec_to_timeout;
-		int			microsec_to_timeout;
 
 		/*
 		 * At the latest stop sleeping once wal_sender_timeout has been
@@ -2053,11 +2051,7 @@ WalSndComputeSleeptime(TimestampTz now)
 													  wal_sender_timeout / 2);
 
 		/* Compute relative time until wakeup. */
-		TimestampDifference(now, wakeup_time,
-							&sec_to_timeout, &microsec_to_timeout);
-
-		sleeptime = sec_to_timeout * 1000 +
-			microsec_to_timeout / 1000;
+		sleeptime = TimestampDifferenceMilliseconds(now, wakeup_time);
 	}
 
 	return sleeptime;